Method for reducing the content of saturated monoglycerides in a raw biodiesel

Abstract

The present invention relates to a method for reducing the content of monoglycerides (MG), also called monoacylglycerides (MAG), especially of saturated monoglycerides (SMG), in a crude biodiesel (CB).

The invention claimed is: 
     
       1. A method for reducing the content of monoglycerides (MG) in a crude biodiesel (CB) which has a content of monoglycerides (MG) of between 0.4% and 0.7% by weight and a content of free fatty acids (FFA) of less than or equal to 0.25% by weight, characterized by the following steps:
 A provision of the crude biodiesel (CB) with the abovementioned ingredients in the abovementioned concentrations; 
 B addition ( 1 ) of an alkaline aqueous solution (S) in the form of sodium hydroxide solution to the crude biodiesel (CB), wherein the NaOH concentration in the sodium hydroxide solution is less than 4.03 mol/l and wherein the amount of sodium hydroxide solution metered in is between 1.0% and 3.0% by weight, based on the amount of crude biodiesel (CB) and 
 wherein the temperature of the crude biodiesel (CB) during the addition of the aqueous alkaline solution (S) is at least 30° C.; 
 C mixing of the alkaline aqueous solution (S) to hydrolyze glycerides in the biodiesel, preferably monoglycerides (MG); 
 wherein the holding time after addition of the aqueous alkaline solution (S) and before the first centrifugal separation ( 2 ) is at least 15 minutes; 
 D first centrifugal separation ( 2 ) of a heavy phase ( 6 ), comprising the alkaline aqueous solution (S) with the hydrolyzed ingredients, from a light phase ( 7 ) comprising the biodiesel by a separator at a speed of 4400 to 7200 rpm; 
 E drying ( 5 ) of the light phase ( 7 ) and/or ( 9 ) to provide a processed biodiesel (PB) for use as fuel with a content of monoglycerides of less than 0.4% by weight, 
 wherein the content of methanol in the biodiesel in steps A-E is less than 0.7% by weight, based on the total weight of crude biodiesel (CB) used or processed biodiesel (PB) in the respective step. 
 
     
     
       2. The method as claimed in  claim 1 , characterized in that, after the centrifugal separation ( 2 ) as per step D and before the drying ( 5 ) as per step E, washing ( 3 ) of the light phase ( 7 ) with water (W) and/or with a dilute acid (A) is effected, as is a second centrifugal separation ( 4 ) of a heavy phase ( 8 ) comprising the water (W) or the dilute acid (A), and any precipitated salts of cations of the alkaline aqueous solution (S) added, from a light phase ( 9 ) comprising the biodiesel. 
     
     
       3. The method as claimed in  claim 1 , characterized in that the NaOH concentration in the sodium hydroxide solution is between 0.51 mol/1 and 2.77 mol/l. 
     
     
       4. The method as claimed in  claim 1 , characterized in that the temperature of the crude biodiesel (CB) during the addition of the aqueous alkaline solution (S) is at least 50° C. 
     
     
       5. The method of  claim 1 , characterized in that the holding time after the addition of the aqueous alkaline solution (S) and before the first centrifugal separation ( 2 ) is 30 to 180 minutes. 
     
     
       6. The method as claimed in  claim 2 , characterized in that the pH of the dilute acid during the washing ( 3 ) is between pH=3 and pH=5. 
     
     
       7. The method as claimed in  claim 2 , characterized in that the dilute acid is a phosphoric and/or citric acid. 
     
     
       8. The method as claimed in  claim 1 , characterized in that the content of methanol in the biodiesel in steps A-E is less than 0.2% by weight based on the total weight of crude biodiesel (CB) used or processed biodiesel (PB) in the respective step. 
     
     
       9. The method as claimed in  claim 1 , characterized in that steps A-E are effected without addition of alcohol to the crude biodiesel or to the intermediate product from the crude biodiesel during the method steps used in the method. 
     
     
       10. The method as claimed in  claim 1 , characterized in that steps A-E are effected without addition of hydrogen to the crude biodiesel or to the intermediate product from the crude biodiesel during the method steps used in the method. 
     
     
       11. The method as claimed in  claim 1 , characterized in that the monoglycerides (MG) are saturated monoglycerides (SMG). 
     
     
       12. The method as claimed in  claim 1 , characterized in that the crude biodiesel (CB) has a content of monoacylglycerides of between 0.41% to 0.69% by weight. 
     
     
       13. The method as claimed in  claim 8 , characterized in that the total alcohol content in the biodiesel in steps A-E is less than 0.2% by weight based on the total weight of crude biodiesel (CB) used or processed biodiesel (PB) in the respective step. 
     
     
       14. The method as claimed in  claim 8 , characterized in that the content of methanol in the biodiesel in steps A-E is less than 0.05% by weight, based on the total weight of crude biodiesel (CB) used or processed biodiesel (PB) in the respective step.